Self-Supported Smart Bacterial Nanocellulose–Phosphotungstic Acid Nanocomposites for Photochromic Applications

Abstract

Bacterial nanocellulose (BNC) is a natural biopolymer obtained by gram-negative bacteria by means of a green and inexhaustible biotechnological process using glucose as producing source. BCN hydrogels is formed by cellulose nanofibrils that maintain an open network structure, an ideal matrix to produce new class of organic-inorganic nanocomposites (OIN) for multifunctional applications. The polyoxometalates (POMs) are complex molecules with several metallic ions sharing oxide ions, forming a highly symmetrical metal oxide cluster. Phosphotungstic acid (PWA), H3PW12O40 photoreduction process activated under ultraviolet irradiation, promoting color change. In this work, photochromic organic-inorganic nanocomposites were prepared by soaking phosphotungstic acid (H3PW12O40) in wet BNC membranes mats at room temperature. Semi-transparent and free-standing BNC/PWA nanocomposite with paper-like aspect were obtained. BNC network was able to control, stabilize and disperse PWA particles in a narrow nanometric distribution, and FTIR spectra indicated that the primary Keggin structure was also preserved in the nanocomposites, independently on the PWA content. The nanoparticles present a narrow distribution of around 16 nm, independently on the PWA concentration. BNC/PWA nanocomposites showed reversible photochromic behavior characteristic of the equilibrium between different tungsten oxidation states. PWA reduction (W6+→ W5+) and organic matrix oxidation is proposed to occur through a radical process involving the interaction of one electron from the oxygen atom of the PWA and one hydrogen from BNC matrix. The photochromic effect vanishes almost completely after 5 h. This mechanism is real in the presence of oxygen, however, if the membranes are left in nitrogen or under vacuum the blue color remains longer than 45 days. Photo-electrochemical behavior was studied by spectroelectrochemistry measurements. It is worth noting that all processes were still reversible in the timescale of the experiment and color changes were observed in several cycles.

Recent progress in polyoxometalate–viologen photochromic hybrids: structural design, photochromic mechanism, and applications

“…Among the known POM-based photochromic hybrids, the common organic ligands such as alkylammonium, multicarboxylic acid and sulfonium cations have been widely studied, and exhibit highly tunable photochromic properties with strong color changes. 38–58 However, the color change in these systems is due to photoreduction of Mo/W 6+ ions through electron transfer inside the POM moiety under UV light, and the organic counter ion only acts as a stabilizer of the reduced POM. 59–62 In recent years, with the in-depth study of viologen-based photochromic compounds, 63–77 researchers have found that electron-deficient viologen ligands are capable of hybridizing with electron-rich POMs; this can not only form hybrid materials with diverse structures, but also bring more outstanding redox properties, photoactivity and thermal stability.…”

Separation of bioethanol using in situ composite membrane of bacterial cellulose/poly (2-acrylamido-2-methylpropane sulfonic acid) (AMPS) and their characterization

“…After incorporation of AMPS to the BC (Fig. 5B), good compatibility and miscibility between BC and AMPS polymers were exhibited on the surface, indicating that the AMPS was uniformly dispersed and embedded in the BC membrane which is supposed to improve its structure to be effectively used in the bioethanol/broth separation process [48,49]. Additionally, the cross-sections of the dried BC membranes in Fig.…”

Scalable, Green, Flexible Photochromic Bacterial Cellulose for Multicolor Switching, Photo‐patterning, and Daily Sunlight UV Monitoring

“…[16,17] In particular, the flexibility, mechanical durability, high porosity, biocompatibility, [18,19] unique 3D porous nanonetwork, and abundant hydroxyl groups are conducive to the permeation and modification of functional materials, making it an ideal substrate for green manufacturing of photochromic smart textiles. [20][21][22] The initial research on preparing photochromic bacterial cellulose (PBC) was conducted by Hu et al [23] and Santos et al [24] ≈10 years ago. Despite extensive exploration of photochromic textiles, modifications based on fermentation products present several critical challenges.…”

“…[ 23 ] and Santos et al. [ 24 ] ≈10 years ago. Despite extensive exploration of photochromic textiles, modifications based on fermentation products present several critical challenges.…”